The State Patrol says it could be weeks before they determine who was at fault in a collision between an ambulance and a car in Renton on Wednesday that killed a 64-year-old woman and seriously injured her granddaughter.

Myong Sun Mun of Seattle was driving her 1999 Honda Accord out of a McDonald’s restaurant parking lot when an ambulance struck her on the driver’s side. She died instantly; her 7-year-old granddaughter is in serious condition at Harborview Medical Center, said Kristin Foley, a spokeswoman.

Investigators said it could be weeks before they determine who was at fault. There are conflicting reports on whether the ambulance had its siren on, in addition to its emergency lights.

At 4:15 p.m., Mun drove out of the fast-food restaurant lot on the east side of Benson Road, across two lanes and into the left-turn lane, headed south. The ambulance was traveling northbound and entered the center turn lane to get past heavy traffic when the vehicles collided.

“Traffic stopped for her so that she could go into the left-turn lane,” State Patrol Sgt. Kirk Merrill said. “That is exactly where the ambulance was on a run.”

Upon impact, Mun’s car crossed all southbound lanes and fell 10 feet down an embankment into a parking lot, skidded 20 feet, then struck another vehicle.

The 24-year-old driver of the ambulance, Jacob Peery, was taking a heart-attack patient to Valley Medical Center and told investigators he had his siren and lights on. Another ambulance brought the patient to the hospital after the crash.

Ambulances are authorized to drive over the speed limit and run red lights and stop signs while responding to an emergency, but it must be done in a safe manner, according to the State Patrol.

“Lights and sirens do not relieve the driver from the duty to drive with regard for the safety of others,” Merrill said. “They must respond cautiously.”

Jay Davidson, owner of Tri-Med, the ambulance company, said the driver had his lights and sirens on, but he doesn’t know how fast he was traveling.

His company also is investigating.

“Everyone is pretty shaken up,” Davidson said.

Mun lived in the Seattle area for about 30 years and often took care of her three grandchildren, said her niece Carolyn Keum of Renton.

“We don’t really know how this happened,” Keum said. “She was just going to McDonald’s.”